Method for operating an internal combustion engine and device for executing the method

ABSTRACT

A method for operating an internal combustion engine and a device for executing the method provide for diagnostics of the exhaust system in which an exhaust-gas treatment device for converting at least one undesirable exhaust gas component is situated. A measure for the conversion is determined from the exhaust gas component, ascertained upstream from the exhaust-gas treatment-device and measured downstream from the exhaust-gas treatment device and compared to a predefinable threshold value. An error signal is issued when the threshold is not met. The approach makes it possible in particular to detect a manipulation in the exhaust system such as the use of a dummy in the exhaust-gas treatment device or, for example, a deliberately defective lining of a component situated in the exhaust-gas treatment device.

FIELD OF THE INVENTION

The present invention is directed to a method for operating an internalcombustion engine, which provides for diagnostics of an exhaust systemin which an exhaust-gas treatment device for converting at least oneundesirable exhaust gas component is situated, and to a device forexecuting the method.

BACKGROUND INFORMATION

German Patent Application No. DE 44 26 020 describes a method in whichthe operational performance of a catalytic converter situated in anexhaust system of an internal combustion engine is monitored. Monitoringis carried out based on the temperature increase which occurs as aresult of the exothermal conversion of oxidizable exhaust gas componentsin the catalytic converter. Two temperature signals are ascertained, thefirst temperature signal being based on a temperature measurementdownstream from the catalytic converter and the second temperaturesignal being calculated using a model.

German Patent Application No. DE 103 58 195 describes a method formonitoring a component situated in an exhaust system of an internalcombustion engine in which the low pass performance, which is determinedby the heat capacity of the component, is checked by analyzing a measureof a first exhaust gas temperature which occurs upstream from thecomponent to be monitored and a second exhaust gas temperature which isdetected by a temperature sensor situated downstream from the componentto be monitored. The described method enables monitoring of thecomponent for a change which may have occurred in the event of impropermanipulation. In the extreme case, the component to be monitored, e.g.,a catalytic converter and/or a particle filter, may have been removedcompletely. Monitoring takes place either during inspections, which mustbe conducted in connection with the maintenance of emission standards,or during regular operation of the internal combustion engine.

A method for operating a catalytic converter used for exhaust emissioncontrol in an internal combustion engine and a device for executing themethod, which provide control or regulation of a reagent fill level inthe catalytic converter to a predefined storage setpoint value, aredescribed in German Patent Application No. DE 10 2004 031 624 (notpreviously published). The targeted pre-definition of the storagesetpoint value ensures that a sufficient reagent quantity is availablein non-stationary operating states of the internal combustion engine forthe preferably complete removal of at least one undesirable exhaustcomponent and that a reagent slip is avoided. Described is a model ofthe catalytic converter which ascertains the reagent fill level in thecatalytic converter based on the reagent flow flowing into the catalyticconverter, possibly based on the NO_(x) mass flow flowing into thecatalytic converter, possibly based on the NO_(x) mass flow exiting thecatalytic converter, and possibly based on a reagent slip.

An object of the present invention is to provide a method for operatingan internal combustion engine which provides for diagnostics of anexhaust system in which an exhaust-gas treatment device for convertingat least one undesirable exhaust gas component is situated, and a devicefor executing the method.

SUMMARY OF THE INVENTION

The method according to the present invention for operating an internalcombustion engine provides for diagnostics of the exhaust system inwhich an exhaust-gas treatment device for converting at least oneundesirable exhaust gas component is situated. From the exhaust gascomponent, ascertained upstream from the exhaust-gas treatment deviceand measured downstream from the exhaust-gas treatment device, a measurefor the conversion is determined and compared to a predefinablethreshold value. An error signal is issued when the threshold is notmet.

The method according to the present invention enables diagnostics of theentire exhaust system. Mechanical defects are detected, for example,which result in the fact that the entire exhaust gas flow does not flowthrough the exhaust-gas treatment device. As long as the exhaust-gastreatment device contains a catalytic converter, it is possible to drawa conclusion about the operational performance of the lining of thecatalytic converter. The approach according to the present inventionmakes it possible in particular to detect a manipulation in the exhaustsystem such as the use of a dummy in the exhaust-gas treatment deviceor, for example, a deliberately defective lining of a component situatedin the exhaust-gas treatment device. Moreover, the complete absence ofthe exhaust-gas treatment device may also be detected.

In the simplest case, the threshold value may be fixedly predefined. Thethreshold value may be set to a value of, for example, 50% of themeasure for the conversion which is expected under normal operatingconditions of the exhaust-gas treatment device. The threshold value ispreferably variable.

In order to localize the error, further diagnostics may be carried outbased on the error signal issued in the event of a threshold shortfall.Furthermore, the error signal may be displayed to prompt a motor vehicledriver to seek a repair shop.

The at least one exhaust gas component, which is detected upstream fromthe exhaust-gas treatment device, e.g., at the intake of the exhaustsystem, may be calculated or measured.

According to one embodiment, the degree of efficiency of the exhaust-gastreatment device is ascertained as a measure for the conversion. Thedegree of efficiency results from the difference between the inflowingand the outflowing exhaust gas component divided by the inflowingexhaust gas component. The concentration of the exhaust gas component inthe exhaust may be used as the basis. Moreover, the mass flow or thevolume flow of the exhaust gas component may be used. The degree ofefficiency of the exhaust-gas treatment device is independent ofabsolute values of the underlying variables.

According to another embodiment, the decrease in the concentration or inthe mass flow/volume flow of the exhaust gas component is ascertained asa measure for the conversion.

According to one embodiment, a measure for the exhaust gas componentupstream from the exhaust-gas treatment device is ascertained from atleast one performance characteristic of the internal combustion engine.A sensor or a mechanical exhaust-gas flap for redirecting exhaust gasflows is no longer necessary due to this measure. The speed of theinternal combustion engine and/or a fuel signal which corresponds to atorque and/or the coolant temperature of the internal combustion engineand/or an exhaust gas recirculation rate and/or other performancecharacteristics may be taken into account as the performancecharacteristic, for example.

According to a corresponding embodiment, the threshold value, to whichthe measure for the conversion is compared, is set based on theoperating conditions prevailing in the exhaust system. For example, thetemperature of the exhaust-gas treatment device and/or the meteredamount of a reagent introduced into the exhaust system and/or theexhaust gas mass flow may be taken into account. If the exhaust-gastreatment device contains at least one catalytic converter, theconversion of the undesirable exhaust gas component depends on thetemperature of the catalytic surfaces, for example. If the reagent,introduced into the exhaust system, is provided for the conversion ofthe undesirable exhaust gas component, the reagent quantity stored inthe catalytic converter and thus the degree of efficiency may beestimated from the metered amount of reagent. Ammonia or, e.g., aurea/water solution as a pre-stage, is provided as the reagent, forexample. In an SCR catalytic converter (selective catalytic reduction),the ammonia converts the NOx emissions of the internal combustionengine.

According to one embodiment, a time delay is provided for delaying theexhaust gas component, measured downstream from the exhaust-gastreatment device, in order to be able to take into account the transfertime of the exhaust gas component in the exhaust system prior to thecomparison with the exhaust gas component ascertained upstream from theexhaust-gas treatment device.

According to one embodiment, the error signal is issued only when thethreshold shortfall lasts at least a predefined period of time.Sporadically occurring errors or errors caused by interference signalsare suppressed using this measure.

The device according to the present invention for operating an internalcombustion engine relates to a control unit which is designed forexecuting the method. The control unit preferably contains at least oneelectrical memory in which the method steps are stored as a computerprogram.

According to a refinement of the device according to the presentinvention, a preferably electrically operable exhaust-gas flap isprovided which applies the exhaust gas component, occurring eitherupstream or downstream from the exhaust-gas treatment device, to asensor for detecting the at least one undesirable exhaust gas component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a technical environment in which a method according to thepresent invention proceeds.

FIG. 2 shows a flow chart of a method according to the presentinvention.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 10, an air detection module12 being situated in its intake area 11 and a reagent metering module 14as well as an exhaust-gas treatment device 15 being situated in itsexhaust system 13. A temperature sensor 16 is assigned to exhaust-gastreatment device 15. An exhaust-gas flap 17 having a first and a secondexhaust gas feed 18, 19 is also situated in exhaust system 13. Firstexhaust gas feed 18 removes exhaust gas upstream from exhaust-gastreatment device 15 and second exhaust gas feed 19 removes exhaust gasdownstream from treatment device 15 and supplies the exhaust gas to anNOx sensor 20. An exhaust gas mass flow msabg occurs in exhaust system13.

Air detection module 12 supplies an air signal msL, internal combustionengine 10 supplies a speed N, temperature sensor 16 supplies atemperature signal TKat, and NOx sensor 20 supplies an NOx signal NOx toa control unit 30.

Control unit 30 supplies a fuel signal mK to a fuel metering device 31which is assigned to internal combustion engine 10. A metering signalascertainment module 32 supplies a reagent metering signal msRea toreagent metering module 14. A conversion ascertainment module 33supplies an actuating signal 34 to exhaust-gas flap 17.

Air signal msL is supplied to conversion ascertainment module 33. Speedsignal N is supplied to an NOx ascertainment module 35 which in turnsupplies an NOx untreated-emission signal NOxvK to metering signalascertainment module 32 as well as to conversion ascertainment module33. Furthermore, a torque signal mi, an exhaust gas recirculation rateagr and a coolant temperature TW are supplied to NOx ascertainmentmodule 35.

Furthermore, reagent metering signal msRea is supplied to an integrator40 which in turn supplies a reagent quantity mRea to metering signalascertainment module 32 and to a threshold value setting module 41.

Temperature signal TKat, provided by temperature sensor 16, is suppliedto metering signal ascertainment module 32 as well as to threshold valuesetting module 41. NOx signal NOx, provided by NOx sensor 20, issupplied to metering signal ascertainment module 32, to conversionascertainment module 33 and to a sensor error ascertainment module 42.

Conversion ascertainment module 33 supplies an actual conversioneta_actual and threshold value setting module 41 supplies a thresholdvalue etaS to a comparator 43. Comparator 43 supplies a switching signal44 to a timer t which provides a first error signal F1. Sensor errorascertainment module 42 provides a second error signal F2.

FIG. 2 shows a flow chart of the method according to the presentinvention. The method starts with a first function block 50 in which NOxsignal NOx is ascertained. NOx ascertainment module 35 ascertains NOxuntreated-emission signal NOxvK in a second function block 51.Conversion ascertainment module 33 ascertains actual conversioneta_actual in a third function block 52. Threshold value setting module41 ascertains threshold value etaS in a fourth function block 53.

In a first query 54, which symbolizes comparator 43, it is determinedwhether actual conversion eta_actual is greater than or at least equalto threshold value etaS. If this is the case, the system jumps back tofirst function block 50. If this not the case, timer t is started infifth function block 55.

In a second query 56, it is checked whether switching signal 44 is stillpresent during the period of time predefined by timer t. If this is notthe case, the system jumps back to first function block 50. If this isthe case, first error signal F1 is provided in a sixth function block56. The possibly present second error signal F2 is subsequently takeninto account in a seventh function block 57.

The method according to the present invention proceeds as follows:

Control unit 30 ascertains fuel signal mK which is supplied to fuelmetering device 31, as a function of speed N of internal combustionengine 10 and the position of an accelerator pedal of a motor vehicle(not shown in greater detail) or possibly as a function of air signalmsL provided by air detection module 12. Fuel signal mK corresponds totorque mi which internal combustion engine 10 should provide or providesalready.

The exhaust gas of internal combustion engine 10 contains at least oneundesirable exhaust gas component which should be reduced by exhaust-gastreatment device 15. As an example, it is assumed in the following thatthe NOx emission of internal combustion engine 10 is the undesirableexhaust gas component.

A catalytic converter, for example, in particular an NOx storagecatalytic converter, which is situated in exhaust-gas treatment device15, is suitable for reducing the NOx emissions of internal combustionengine 10. It is assumed in the exemplary embodiment that the catalyticconverter situated in exhaust-gas treatment device 15 is an SCRcatalytic converter (selective catalytic reduction) which uses a reagentto convert the NOx contained in the exhaust gas. Ammonia may be providedas the reagent which may be obtained from a urea/water solution which isinserted into exhaust system 13 by reagent metering module 14.

The reagent flow is set via reagent metering signal msRea which is setby metering signal ascertainment module 32 as a function of NOxuntreated-emission signal NOxvK, for example, which is provided by NOxascertainment module 35. Via this measure, the reagent flow is adjustedto the NOx, and inserted into exhaust system 13 by internal combustionengine 10. NOx signal Nox, provided by NOx sensor 20 as a function ofthe NOx concentration downstream from exhaust-gas treatment device 15,may be used additionally or alternatively for setting reagent meteringsignal msRea. Furthermore, the reagent quantity, which is ascertained byintegrator 40 via variable integration of reagent metering signal msRea,may be taken into account. Moreover, the temperature of the SCRcatalytic converter which is detected by temperature sensor 16 whichprovides temperature signal Tkat may be taken into account inparticular.

Temperature sensor 16 preferably detects the exhaust gas temperaturedirectly upstream from exhaust-gas treatment device 15. If needed,temperature sensor 16 may be situated inside of exhaust-gas treatmentdevice 15.

NOx sensor 20, which provides NOx signal NOx, detects at least the NOxconcentration in the exhaust gas downstream from exhaust-gas treatmentdevice 15. The shown exemplary embodiment provides exhaust-gas flap 17which applies to NOx sensor 20 either exhaust gas from downstream fromexhaust-gas treatment device 15 or exhaust gas from upstream fromexhaust-gas treatment device 15. Exhaust-gas flap 17, actuated as afunction of actuating signal 34 which is provided by conversionascertainment module 33, establishes a connection between the exhaustgas and NOx sensor 20 either via first exhaust gas feed 18 or via secondexhaust gas feed 19. Therefore, with the aid of exhaust-gas flap 17, NOxsensor 20 is able to detect the NOx concentration in the exhaust gaseither upstream or downstream from exhaust-gas treatment device 15.

The NOx emissions of internal combustion engine 10 may be ascertained byNOx ascertainment module 35 from performance characteristics of internalcombustion engine 10 and provided as NOx untreated-emission signalNOxvK. The NOx concentration may alternatively or additionally bemeasured upstream from exhaust-gas treatment device 15. As describedabove, an additional NOx sensor may be avoided due to the use ofexhaust-gas flap 17. A plausibility check of the detected values may beperformed by ascertaining the NOx emissions of internal combustionengine 10 in multiple ways.

For executing the method according to the present invention, it isprovided to ascertain the at least one undesirable exhaust gas componentupstream and downstream from exhaust-gas treatment device 15 accordingto the first two function blocks 50, 51. At least one measure for actualconversion eta_actual of the exhaust gas component is subsequentlyascertained in conversion ascertainment module 33.

Conversion ascertainment module 33 preferably ascertains the degree ofefficiency of the conversion of the exhaust gas component. The degree ofefficiency results from the difference between the exhaust gas componentflowing into exhaust-gas treatment device 15 and the exhaust gascomponent flowing out of exhaust-gas treatment device 15 divided by theinflowing exhaust gas component. This may be based on the concentrationof the exhaust gas component or on the absolute values such as the massflow or the volume flow of the exhaust gas component.

Instead of ascertaining the degree of efficiency, conversionascertainment module 33 may base the ascertainment of at least onemeasure for the conversion of the at least one undesirable exhaust gascomponent on absolute variables such as the difference of the mass flowor the volume flow.

Conversion ascertainment module 33 preferably contains a time delay fordelaying the exhaust gas component, measured downstream from exhaust-gastreatment device 15, in order to be able to take into account thetransfer time of the exhaust gas component in exhaust system 13 prior tothe comparison in comparator 43 with the exhaust gas componentascertained upstream from exhaust-gas treatment device 15.

According to fourth function block 53, threshold value etaS is set inthreshold value setting module 41. In a simple embodiment, thresholdvalue etaS may be set as a fixed value, e.g., 50% of a minimallyexpected actual conversion eta_actual. Threshold value etaS ispreferably set as a function of operating conditions of internalcombustion engine 10 and in particular as a function of operatingconditions in exhaust system 13.

Threshold value etaS may initially depend on the temperature ofexhaust-gas treatment device 15 which may be estimated or which ispreferably measured by temperature sensor 16, at least approximately. Inparticular when exhaust-gas treatment device 15 contains an SCRcatalytic converter, threshold value etaS is preferably set by thereagent stored in the SCR catalytic converter, the temperature of theSCR catalytic converter preferably also being taken into account, sincethe storage capability of an SCR catalytic converter with respect to thereagent depends on the temperature. In particular, exhaust gas mass flowmsabg which is preferably calculated from performance characteristics ofinternal combustion engine 10 such as speed N and/or fuel signal mKand/or air signal msL may be additionally or alternatively taken intoaccount.

Actual conversion eta_actual and threshold value etaS are supplied tocomparator 43. According to first query 54, comparator 43 determineswhether the measure for the actual conversion corresponds at leastequally to threshold value etaS. If this is the case, the system jumpsback to first function block 50 since the diagnostics did not yield anunusual result. However, if this is the case, comparator 43 providesswitching signal 44 which is supplied to timer t.

According to fifth function block 55, switching signal 44 starts timert. Second query 56 checks in timer t whether switching signal 44 isstill present within the period of time predefined by timer t. If thisis not the case, the system jumps back to first function block 50 sincethe diagnostics yielded only a sporadically occurring error or respondeddue to incidentally present interference signals. If switching signal 44is still present after the period of time predefined by timer t haselapsed, first error signal F1 is provided according to sixth functionblock 56.

First error signal F1 may be displayed, for example, to signal to adriver of a motor vehicle that a stop at a repair shop is necessary.First error signal F1 is preferably stored in an error memory (not shownin greater detail) and/or is used preferably to start further diagnosticprocedures.

First error signal F1 states that an error has occurred in exhaustsystem 13. An error may be caused, for example, when the exhaust gasflow in exhaust system 13 through exhaust-gas treatment device 15 is atleast partially interrupted. This may occur, for example, due to adefective exhaust pipe between internal combustion engine 10 andexhaust-gas treatment device 15. Another error possibility may bepresent in exhaust-gas treatment device 15. A cleaning effect ofexhaust-gas treatment device 15 with respect to the at least oneundesirable exhaust gas component may have deteriorated over time, forexample. Another possibility, which the method according to the presentinvention detects with great reliability, is based upon illegaltampering with exhaust system 13 which may mean, for example, that,instead of a proper exhaust-gas treatment device 15, a dummy has beeninstalled, or that a lining of a catalytic converter, situated inexhaust-gas treatment device 15, has deliberately been completed in ashoddy manner.

Another error possibility is that NOx signal NOx, provided by NOx sensor20, is erroneous. In the shown exemplary embodiment, an occurring errorin NOx sensor 20 may be specifically searched for in sensor errorascertainment module 42. Due to the possibility of multiple errorcauses, an advantageous refinement of the approach according to thepresent invention provides that after the occurrence of first errorsignal F1, further measures are initially taken to localize the error.

1. A method for operating an internal combustion engine which providesfor diagnostics of an exhaust system of the internal combustion engine,in which an exhaust-gas treatment device for converting at least oneundesirable exhaust gas component is situated, the method comprising:determining a measure for the conversion from the exhaust gas component,ascertained upstream from the exhaust-gas treatment device and measureddownstream from the exhaust-gas treatment device; comparing the measureto a predefined threshold value; and providing an error signal when thethreshold value is not met.
 2. The method according to claim 1, whereina degree of efficiency of the exhaust-gas treatment device isascertained as a measure for the conversion.
 3. The method according toclaim 1, wherein a reduction of a concentration of the exhaust gascomponent is ascertained as a measure for the conversion.
 4. The methodaccording to claim 1, wherein a measure for the exhaust gas componentupstream from the exhaust-gas treatment device is calculated fromperformance characteristics of the internal combustion engine.
 5. Themethod according to claim 1, wherein the threshold value is set basedupon at least one of (a) operating conditions in the exhaust system and(b) operating conditions of the internal combustion engine.
 6. Themethod according to claim 5, wherein at least one of a temperature ofthe exhaust-gas treatment device and a metering of a reagent introducedinto the exhaust system is taken into account.
 7. The method accordingto claim 1, wherein a delay time for delaying the exhaust gas componentmeasured downstream from the exhaust-gas treatment device is provided inorder to take into account a transit time of the exhaust gas componentin the exhaust system.
 8. The method according to claim 1, wherein theerror signal is provided when a threshold shortfall lasts at least apredefined period of time.
 9. The method according to claim 1, whereinthe exhaust gs component includes NOx emissions of the internalcombustion engine.
 10. The method according to claim 1, furthercomprising carrying out further diagnostic procedures after the errorsignal occurs.
 11. A device for operating an internal combustion engine,which provides for diagnostics of an exhaust system of the internalcombustion engine, in which an exhaust-gas treatment device forconverting at least one undesirable exhaust gas component is situated,the device comprising at least one control unit for performing thefollowing: determining a measure for the conversion from the exhaust gascomponent, ascertained upstream from the exhaust-gas treatment deviceand measured downstream from the exhaust-gas treatment device; comparingthe measure to a predefined threshold value; and providing an errorsignal when the threshold value is not met.
 12. The device according toclaim 11, further comprising a sensor for detecting the at least oneundesirable exhaust gas component, and wherein an exhaust-gas flapapplies the exhaust gas component occurring one of upstream anddownstream from the exhaust-gas treatment device to the sensor.